Conventionally, a semiconductor device in which a bonding pad is disposed directly over semiconductor elements is known. For example, Patent Document 1 has disclosed a semiconductor device which has a substrate, semiconductor elements formed on the semiconductor substrate, a base layer of an Al-based material, a barrier layer and a joining layer on which a bonding wire of an Au-based material is thermally pressed. The base layer, the barrier layer and the joining layer are laminated in this order.